Heart failure is a pathophysiological condition in which the heart is unable to pump blood at a rate commensurate with the requirement of the metabolizing tissues or can do so only from an elevated filling pressure (increased load). Thus, the heart has a diminished ability to keep up with its workload. Over time, this condition leads to excess fluid accumulation, such as peripheral edema, and is referred to as congestive heart failure.
When an excessive pressure or volume load is imposed on a ventricle, myocardial hypertrophy (i.e., enlargement of the heart muscle) develops as a compensatory mechanism. Hypertrophy permits the ventricle to sustain an increased load because the heart muscle can contract with greater force. However, a ventricle subjected to an abnormally elevated load for a prolonged period eventually fails to sustain an increased load despite the presence of ventricular hypertrophy, and pump failure may ultimately occur.
Heart failure can arise from any disease that affects the heart and interferes with circulation. For example, a disease that increases the heart muscle's workload, such as hypertension, will eventually weaken the force of the heart's contraction. Hypertension is a condition in which there is an increase in resistance to blood flow through the vascular system. This resistance leads to increases in systolic and/or diastolic blood pressures. Hypertension places increased tension to the left ventricular myocardium, causing it to stiffen and hypertrophy, and accelerates the development of atherosclerosis in the coronary arteries. The combination of increased demand and lessened supply increases the likelihood of myocardial ischemia leading to myocardial infarction, sudden death, arrhythmias, and congestive heart failure.
Ischemia is a condition in which an organ or a part of the body fails to receive a sufficient blood supply. When an organ is deprived of its blood supply, it is said to be hypoxic. An organ will become hypoxic even when the blood supply temporarily ceases, such as during a surgical procedure or during temporary artery blockage. Ischemia initially leads to a decrease in or loss of contractile activity. When the organ affected is the heart, this condition is known as myocardial ischemia, and myocardial ischemia initially leads to abnormal electrical activity. This may generate an arrhythmia. When myocardial ischemia is of sufficient severity and duration, cell injury may progress to cell death—i.e., myocardial infarction—and subsequently to heart failure, hypertrophy, or congestive heart failure.
When blood flow resumes to an organ after temporary cessation, this is known as ischemic reperfusion of the organ. For example, reperfusion of an ischemic myocardium may counter the effects of coronary occlusion, a condition that leads to myocardial ischemia. Ischemic reperfusion to the myocardium may lead to reperfusion arrhythmia or reperfusion injury. The severity of reperfusion injury is affected by numerous factors, such as, for example, duration of ischemia, severity of ischemia, and speed of reperfusion. Conditions observed with ischemia reperfusion injury include neutrophil infiltration, necrosis, and apoptosis.
Drug therapies, using known active ingredients such as vasodilators, angiotensin II receptor antagonists, angiotensin converting enzyme inhibitors, diuretics, antithrombolytic agents, β-adrenergic receptor antagonists, α-adrenergic receptor antagonists, calcium channel blockers, and the like, are available for treating heart failure and associated diseases. Of course, any drug used for treatment may result in side effects. For example, vasodilators may result in hypotension, myocardial infarction, and adverse immune response. Angiotensin II receptor antagonists and angiotensin converting enzyme inhibitors are often associated with acute renal failure, fetopathic potential, proteinuria, hepatotoxicity, and glycosuria as side effects. Similarly, common side effects associated with calcium channel blockers include hypotension, peripheral edema, and pulmonary edema. β-Adrenergic receptor antagonists and diuretics have been associated with incompatibility with nonsteroidal anti-inflammatory drugs in addition to impotence, gout, and muscle cramps in the case of diuretics and in addition to a decrease in left ventricular function and sudden withdrawal syndrome in the case of β-adrenergic receptor antagonists. Moreover, side effects associated with α-adrenergic receptor antagonists include thostatic hypotension, and side effects associated with antithrombolytic agents include excessive bleeding.
To address the side effects, the dosage of a drug may be reduced or the administration of the drug may be abated and replaced with another drug. It would be desirable to administer a drug therapy with decreased amounts of the active ingredient to reduce side effects but maintain effectiveness.